This may sound like a stupid question, but exactly how does a cold air intake work vs. the stock intake? What are the recommended brands of good cold air intakes? Thanks.

2000 SVT Contour (Tropic Green) -Toyo Proxes T1-S's (215/45 ZR 17) -17x7 Emkei RS5 Wheels -Sylvania SilverStars (High and low beams) -Pioneer DEH-P4400 -Pioneer TS-A6867's (front and back) -K&N Air Filter